Preoperatively planning an arthroplasty procedure and generating a corresponding patient specific arthroplasty resection guide

ABSTRACT

Methods of manufacturing a custom arthroplasty resection guide or jig are disclosed herein. For example, one method may include: generating MRI knee coil two dimensional images, wherein the knee coil images include a knee region of a patient; generating MRI body coil two dimensional images, wherein the body coil images include a hip region of the patient, the knee region of the patient and an ankle region of the patient; in the knee coil images, identifying first locations of knee landmarks; in the body coil images, identifying second locations of the knee landmarks; run a transformation with the first and second locations, causing the knee coil images and body coil images to generally correspond with each other with respect to location and orientation.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/084,255, filed Nov. 19, 2013, which is a continuation ofU.S. patent application Ser. No. 13/086,275 (“the '275 application”),filed Apr. 13, 2011, and titled “Preoperatively Planning an ArthroplastyProcedure and Generating a Corresponding Patient Specific ArthroplastyResection Guide,” now U.S. Pat. No. 8,617,171. The '275 application is acontinuation-in-part (“CIP”) of U.S. patent application Ser. No.12/760,388 (“the '388 application”), filed Apr. 14, 2010, now U.S. Pat.No. 8,737,700.

The '388 application is a CIP application of U.S. patent applicationSer. No. 12/563,809 (“the '809 application), filed Sep. 21, 2009, andtitled “Arthroplasty System and Related Methods,” now U.S. Pat. No.8,545,509, which claims priority to U.S. patent application 61/102,692(“the '692 application”), filed Oct. 3, 2008, and titled “ArthroplastySystem and Related Methods.” The '388 application is also a CIPapplication of U.S. patent application Ser. No. 12/546,545 (“the 545application”), filed Aug. 24, 2009, and titled “Arthroplasty System andRelated Methods,” now U.S. Pat. No. 8,715,291, which claims priority tothe '692 application.

The '545 application is also a CIP application of U.S. patentapplication Ser. No. 12/111,924 (“the '924 application”), filed Apr. 29,2008, and titled “Generation of a Computerized Bone Model Representativeof a Pre-Degenerated State and Useable in the Design and Manufacture ofArthroplasty Devices,” now U.S. Pat. No. 8,480,679. The '545 applicationis also a CIP application of U.S. patent application Ser. No. 11/959,344(“the '344 application), filed Dec. 18, 2007, and titled “System andMethod for Manufacturing Arthroplasty Jigs,” now U.S. Pat. No.8,221,430.

The '809 application is a CIP application of U.S. patent applicationSer. No. 12/505,056 (“the '056 application”), filed Jul. 17, 2009, andtitled “System and Method for Manufacturing Arthroplasty Jigs HavingImproved Mating Accuracy,” now U.S. Pat. No. 8,777,875. The '056application claims priority to U.S. patent application 61/083,053, filedJul. 23, 2008, and titled “System and Method for ManufacturingArthroplasty Jigs Having Improved Mating Accuracy.” The '809 applicationis also a CIP application of the '924 application. The '809 applicationis also a CIP application of the '344 application.

The present application claims priority to all of the above mentionedapplications and hereby incorporates by reference all of theabove-mentioned applications in their entireties into the presentapplication.

FIELD OF THE INVENTION

The present invention relates to systems and methods for manufacturingcustomized arthroplasty cutting jigs. More specifically, the presentinvention relates to automated systems and methods of manufacturing suchjigs.

BACKGROUND OF THE INVENTION

Over time and through repeated use, bones and joints can become damagedor worn. For example, repetitive strain on bones and joints (e.g.,through athletic activity), traumatic events, and certain diseases(e.g., arthritis) can cause cartilage in joint areas, which normallyprovides a cushioning effect, to wear down. When the cartilage wearsdown, fluid can accumulate in the joint areas, resulting in pain,stiffness, and decreased mobility.

Arthroplasty procedures can be used to repair damaged joints. During atypical arthroplasty procedure, an arthritic or otherwise dysfunctionaljoint can be remodeled or realigned, or an implant can be implanted intothe damaged region. Arthroplasty procedures may take place in any of anumber of different regions of the body, such as a knee, a hip, ashoulder, or an elbow.

One type of arthroplasty procedure is a total knee arthroplasty (“TKA”),in which a damaged knee joint is replaced with prosthetic implants. Theknee joint may have been damaged by, for example, arthritis (e.g.,severe osteoarthritis or degenerative arthritis), trauma, or a raredestructive joint disease. During a TKA procedure, a damaged portion inthe distal region of the femur may be removed and replaced with a metalshell, and a damaged portion in the proximal region of the tibia may beremoved and replaced with a channeled piece of plastic having a metalstem. In some TKA procedures, a plastic button may also be added underthe surface of the patella, depending on the condition of the patella.

Implants that are implanted into a damaged region may provide supportand structure to the damaged region, and may help to restore the damagedregion, thereby enhancing its functionality. Prior to implantation of animplant in a damaged region, the damaged region may be prepared toreceive the implant. For example, in a knee arthroplasty procedure, oneor more of the bones in the knee area, such as the femur and/or thetibia, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) toprovide one or more surfaces that can align with the implant and therebyaccommodate the implant.

Accuracy in implant alignment is an important factor to the success of aTKA procedure. A one- to two-millimeter translational misalignment, or aone- to two-degree rotational misalignment, may result in imbalancedligaments, and may thereby significantly affect the outcome of the TKAprocedure. For example, implant misalignment may result in intolerablepost-surgery pain, and also may prevent the patient from having full legextension and stable leg flexion.

To achieve accurate implant alignment, prior to treating (e.g., cutting,drilling, reaming, and/or resurfacing) any regions of a bone, it isimportant to correctly determine the location at which the treatmentwill take place and how the treatment will be oriented. In some methods,an arthroplasty jig may be used to accurately position and orient afinishing instrument, such as a cutting, drilling, reaming, orresurfacing instrument on the regions of the bone. The arthroplasty jigmay, for example, include one or more apertures and/or slots that areconfigured to accept such an instrument.

A system and method has been developed for producing customizedarthroplasty jigs configured to allow a surgeon to accurately andquickly perform an arthroplasty procedure that restores thepre-deterioration alignment of the joint, thereby improving the successrate of such procedures. Specifically, the customized arthroplasty jigsare indexed such that they matingly receive the regions of the bone tobe subjected to a treatment (e.g., cutting, drilling, reaming, and/orresurfacing). The customized arthroplasty jigs are also indexed toprovide the proper location and orientation of the treatment relative tothe regions of the bone. The indexing aspect of the customizedarthroplasty jigs allows the treatment of the bone regions to be donequickly and with a high degree of accuracy that will allow the implantsto restore the patient's joint to a generally pre-deteriorated state.

It is believed that it is best for the vast majority of patients to havethe patient's joint restored to its pre-deteriorated state (i.e.,natural (i.e., kinematic) alignment). However, for some patient's, itmay not be possible or desirable to restore the patient's joint to itnatural (i.e., kinematic) alignment. For example, a physician maydetermine that the patient's joint assume a zero degree mechanical axisalignment or an alignment between the zero degree mechanical axisalignment and the natural (i.e., kinematic) alignment.

There is a need in the art for a system and method capable of generatingcustomized arthroplasty jigs configured for a variety of alignmentresults. There is also a need in the art for a system and method capableof communicating joint alignment information to a physician andincorporating into the jig design the physician's input regarding thealignment information.

SUMMARY

Various embodiments of a method of manufacturing a custom arthroplastyresection guide or jig are disclosed herein. In a first embodiment, themethod may include: generate MRI knee coil two dimensional images,wherein the knee coil images include a knee region of a patient;generate MRI body coil two dimensional images, wherein the body coilimages include a hip region of the patient, the knee region of thepatient and an ankle region of the patient; in the knee coil images,identify first locations of knee landmarks; in the body coil images,identify second locations of the knee landmarks; run a transformationwith the first and second locations, causing the knee coil images andbody coil images to generally correspond with each other with respect tolocation and orientation.

In a second embodiment, the method may include: preoperatively plan in athree dimensional computer environment a proposed post-surgical jointgeometry for a joint, wherein the proposed post-surgical joint geometryis a natural (i.e., kinematic) alignment joint geometry that isgenerally representative of the joint prior to degeneration; provide atwo dimensional coronal view of the proposed post-surgical jointgeometry to a physician; employ feedback received from the physicianregarding the two dimensional coronal view to arrive at a finalizedpost-surgical joint geometry that is at least one of: a) the naturalalignment joint geometry; b) a zero degree mechanical axis alignmentjoint geometry, or somewhere between a) and b).

In a third embodiment, the method may include: a) identity in a computerenvironment hip, knee and ankle centers in a first set of twodimensional images; b) generate in a computer environment a threedimensional knee model from a second set of two dimensional images; c)cause the three dimensional knee model and hip, knee and ankle centersto be positioned relative to each other in a global coordinate systemgenerally as if the three dimensional knee model were generated from thefirst set of two dimensional images; d) preoperatively plan anarthroplasty procedure with the three dimensional knee model of step c);and e) at least one of maintain or reestablish the positionalrelationship established in step c) between the three dimensional kneemodel and the hip, knee and ankle centers to address any positionalchanges in the global coordinate system for the three dimensional kneemodel during the preoperatively planning of step d).

In a fourth embodiment, the method may include: a) generating a threedimensional femur bone model from MRI knee coil two dimensional images,wherein the knee coil images include a knee region of a patient; b)identifying a hip center and a femur knee center in MRI body coil twodimensional images, wherein the body coil images include a hip region ofthe patient and the knee region of the patient; c) causing the threedimensional femur bone model and hip center and femur knee center togenerally correspond with each other with respect to location andorientation; d) defining relative to the three dimensional femur bonemodel a femoral mechanical axis via the femur knee center and the hipcenter; e) identifying a most distal condylar point of the threedimensional femur bone model; f) defining a distal plane that isorthogonal to the femoral mechanical axis in a coronal view of the threedimensional femur bone model, wherein the distal plane also passesthrough the most distal condylar point; g) and defining a resectionplane that is parallel to the distal plane and proximally offset fromthe distal plane; and h) using data associated with the resection planeto define a resection guide in the custom arthroplasty resection guide.

In a fifth embodiment, the method may include: a) generating a threedimensional tibia bone model from MRI knee coil two dimensional images,wherein the knee coil images include a knee region of a patient; b)identifying an ankle center and a tibia knee center in MRI body coil twodimensional images, wherein the body coil images include an ankle regionof the patient and the knee region of the patient; c) causing the threedimensional tibia bone model and ankle center and tibia knee center togenerally correspond with each other with respect to location andorientation; d) defining relative to the three dimensional tibia honemodel a tibial mechanical axis via the tibia knee center and the anklecenter; e) identifying a condylar point of the three dimensional tibiabone model; f) defining a proximal plane that is orthogonal to thetibial mechanical axis in a coronal view of the three dimensional tibiabone model, wherein the proximal plane also passes through a condylarpoint; g) defining a resection plane that is parallel to the proximalplane and distally offset from the proximal plane; and h) using dataassociated with the resection plane to define a resection guide in thecustom arthroplasty resection guide.

In a sixth embodiment, the method may include: a) identify in a computerenvironment hip, knee and ankle centers in a first set of twodimensional images; b) generate in a computer environment a threedimensional knee model from a second set of two dimensional images; c)cause the three dimensional knee model and hip, knee and ankle centersto be positioned relative to each other in a global coordinate systemgenerally as if the three dimensional knee model were generated from thefirst set of two dimensional images; d) preoperatively plan anarthroplasty procedure with the three dimensional knee model of step c)via a method including: i) defining a mechanical axis relative to thethree dimensional knee model via a pair of points including the kneecenter and at least one of the hip center or ankle center; and ii)defining a resection plane parallel to, and offset from, a referenceplane that: 1) is orthogonal to the mechanical axis in a coronal viewand 2) extends through a condylar point on the three dimensional kneemodel; and e) using data associated with the resection plane to define aresection guide in the custom arthroplasty resection guide.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various aspects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a system for employing the automatedjig production method disclosed herein.

FIGS. 1B-1K are flow chart diagrams outlining the jig production methoddisclosed herein.

FIGS. 1L-1M are flow chart diagrams outlining an alternative embodimentof a portion of the jig production method disclosed herein.

FIGS. 2A and 2B are, respectively, bottom and top perspective views ofan example customized arthroplasty femur jig.

FIGS. 3A and 3B are, respectively, bottom and top perspective views ofan example customized arthroplasty tibia jig.

FIG. 4 is a coronal view of a patient's leg having a zero-degreemechanical axis knee joint geometry.

FIG. 5 is a coronal view of a patient's leg having a varus knee jointgeometry.

FIG. 6 is an isometric view of the patient's leg bone structureillustrating knee coil images.

FIG. 7 is an isometric view of the patient's leg bone structureillustrating body coil images.

FIG. 8 is a coronal 2D knee coil image with points identified onlandmarks of the knee region of the femur.

FIG. 9 is a coronal 2D knee coil image with points identified onlandmarks of the knee region of the tibia.

FIG. 10 is a coronal 2D body coil image with points identified onlandmarks of the knee region of the femur.

FIG. 11 is a coronal 2D body coil image with points identified onlandmarks of the knee region of the tibia.

FIG. 12 is a diagrammatic depiction of the femur 2D knee coil imagesbeing transformed to the femur 2D body coil images.

FIG. 13 is a diagrammatic depiction of the tibia 2D knee coil imagesbeing transformed to the tibia 2D body coil images.

FIG. 14 is a coronal 2D body coil image of the hip with the center ofthe femoral head indicated.

FIG. 15 is a coronal 2D knee coil image of the knee with the centers ofthe femur and tibia indicated.

FIG. 16 is a coronal 2D body coil image of the ankle with the center ofthe ankle joint indicated.

FIG. 17 is a coronal snapshot of the restored bone models, the implantmodels, the joint center points, and the femur mechanical axis, thetibia mechanical axis and the mechanical axis.

FIG. 18 is another version of the 2D coronal snapshot that may beprovided to the physician.

FIG. 19 is a diagrammatic depiction of the axes and their relationshipto each other in the global coordinate system.

FIG. 20 is a diagrammatic depiction of a process of adjusting resectionlines based on joint geometry information conveyed via the 2D coronalsnapshots.

FIG. 21 is coronal view of 3D planning or bone models.

FIG. 22 is a coronal-sagittal isometric view of 3D overestimatedarthritic models.

FIG. 23 is a coronal view of a 3D femoral superimposed model formed ofthe 3D femoral bone and overestimated arthritic models superimposed.

FIG. 24 is an axial view of the 3D femoral superimposed model of FIG.23.

FIG. 25 is a coronal view of a 3D tibial superimposed model formed ofthe 3D tibial bone and overestimated arthritic models superimposed.

FIG. 26 is an axial view of the 3D tibial superimposed model of FIG. 25.

FIG. 27 is a coronal view of the 3D femoral bone model with thesuperior/inferior depth of resection depicted to achieve the desiredvarus/valgus resection orientation.

FIG. 28 is a coronal view of the 3D tibial superimposed model (i.e., 3Dtibial bone model superimposed with the 3D tibial arthritic model) withthe superior/inferior depth of resection depicted to achieve the desiredvarus/valgus resection orientation.

FIG. 29 is a sagittal view of the 3D femoral bone model with theflexion/extension orientation depicted.

FIG. 30 is a sagittal view of the 3D tibial superimposed model with theflexion/extension orientation depicted.

FIG. 31 is an axial or transverse view of the 3D femoral bone model withthe external/internal orientation depicted.

FIG. 32 is a coronal view of the 3D femoral bone model superimposed witha 3D femoral implant model with the superior/inferior translationdepicted.

FIG. 33 is a sagittal view of the 3D femoral bone model superimposedwith a 3D femoral implant model with the anterior/posterior translationdepicted and flexion/extension depicted.

FIG. 34 is a sagittal view of the 3D tibial bone model superimposed witha 3D tibial implant model with the superior/inferior translationdepicted and flexion/extension (i.e., tibial slope depicted).

FIG. 35 is an axial or transverse view of the 3D femoral bone modelsuperimposed with a 3D femoral implant model with the medial/lateraltranslation depicted.

FIG. 36 is an axial or transverse view of the 3D tibial bone modelsuperimposed with a 3D tibial implant model with the medial/lateral andanterior/posterior translations depicted.

DETAILED DESCRIPTION

Disclosed herein are customized arthroplasty jigs 2 and systems 4 for,and methods of, producing such jigs 2. The jigs 2 are customized to fitspecific bone surfaces of specific patients. Depending on the embodimentand to a greater or lesser extent, the jigs 2 are automatically plannedand generated and may be similar to those disclosed in these three U.S.patent applications: U.S. patent application Ser. No. 11/656,323 to Parket al., titled “Arthroplasty Devices and Related Methods” and filed Jan.19, 2007; U.S. patent application Ser. No. 10/146,862 to Park et al.,titled “Improved Total Joint Arthroplasty System” and filed May 15,2002; and U.S. patent Ser. No. 11/642,385 to Park et al., titled“Arthroplasty Devices and Related Methods” and filed Dec. 19, 2006. Thedisclosures of these three U.S. patent applications are incorporated byreference in their entireties into this Detailed Description.

The methods and systems disclosed herein allow a resulting jig 2 togenerate surgical resections that allow implanted arthroplastyprosthetic femoral and tibial joint components to achieve a jointalignment that is: (1) generally representative of the patient'spre-degenerative joint line; generally corresponding to a zeromechanical axis alignment; or (3) somewhere between (1) and (2). Whetherthe resections result in a joint alignment that is (1), (2) or somewherebetween (1) and (2) may be a result of physician input and modificationof the natural (i.e., kinematic) joint alignment calculated duringpreoperative planning (“POP”).

As can be understood from FIG. 4, which is a coronal view of a patient'sleg 200, in zero-degree mechanical axis theory, the center of the hip202 (located at the head 204 of the femur 206), the center of the knee208 (located at the notch where the intercondylar tubercle of the tibia210 meets the femur 206), and the center of ankle 212 form a straightline which defines the mechanical axis (“MA”) 214 of the leg skeletalstructure. As a result, the femoral mechanical axis (“FMA”) 216, whichextends from the hip center 202 to the knee center 208, is coextensivelyaligned with the MA 214. Similarly, the tibial mechanical axis (TMA”)218, which extends from the knee center 208 to the ankle center 212, iscoextensively aligned with the MA 214. When the patient's leg 200 isstanding in full extension and viewed from the front, the MA 214. FMA216 and TMA 218 are perpendicular to the hip center axis 220, the kneejoint line axis 222, and the ankle center axis 224.

In reality, only approximately two percent of the human population hasthe zero-degree mechanical axis (“neutral”) leg skeletal structuredepicted in FIG. 4. The other approximately 98 percent of the humanpopulation has a leg skeletal structure that is slightly varus (bowlegged), as depicted in FIG. 5, or slightly valgus (knocked knee). Thus,for such varus or valgus leg skeletal structures, the FMA 214 and TMA216 will not be coextensively aligned with the MA 214 or perpendicularto the knee joint line axis 222.

A knee arthroplasty procedure may be considered a natural alignment orkinematic alignment procedure when the knee arthroplasty procedure ispreoperatively planned such that the prosthetic knee implants implantedduring the knee arthroplasty procedure generally return the patient'sknee geometry to the geometry that existed before the patient's kneegeometry was impacted via deterioration of the knee joint. For example,if the patient's pre-deteriorated knee geometry was varus, such asdepicted in FIG. 5, then the knee arthroplasty procedure ispreoperatively planned such that the implanted prosthetic knee implantsresult in a knee geometry that is generally the same extent varus.Similarly, if the patient's pre-deteriorated knee geometry was valgus,then the knee arthroplasty procedure is preoperatively planned such thatthe implanted prosthetic knee implants result in a knee geometry that isgenerally the same extent valgus. Finally, if the patient'spre-deteriorated knee geometry was neutral such as depicted in FIG. 4,then the knee arthroplasty procedure is preoperatively planned such thatthe implanted prosthetic knee implants result in a knee geometry that isgenerally neutral.

In natural or kinematic alignment, the goal may be to create aprosthetic knee joint line 222 that recreates the patient'spre-degenerated knee joint line 222, which may have been parallel to theground during a two legged stance in the frontal plane (feetapproximated and parallel to the ground during gait). Studies suggestthat with the feet approximated in two-legged stance, the joint line isparallel to the ground, and the mechanical axis is positioned with a twoto three degree inward inclination.

A knee arthroplasty procedure may be considered a zero-degree mechanicalaxis or neutral alignment procedure when the knee arthroplasty procedureis preoperatively planned such that the prosthetic knee implantsimplanted during the knee arthroplasty procedure generally result in aneutral knee geometry for the patient, regardless of whether thepatient's pre-deteriorated knee geometry was varus, valgus or neutral.In zero-degree mechanical axis alignment, the goal may be to create aprosthetic knee joint line 222 that is perpendicular to the TMA 218, theTMA 218 coinciding with the MA 214.

A patient's natural pre-degenerated knee geometry may have served thepatient well prior to knee joint degeneration. However, a physician maydetermine that it is in the patient's best interest to receive apost-surgical knee geometry that is a natural alignment, neutralalignment, or something in between, depending on the physician'sassessment of the patient's deteriorated bone geometry and condition,the applicability of available prosthetic implants, and other factors.Consequently, there is a need for the systems and methods disclosedherein.

To provide an overall understanding of the systems 4 for, and methodsof, producing the customized arthroplasty jigs 2, reference is made toFIGS. 1A-1K. FIG. 1A is a schematic diagram of a system 4 for employingthe automated jig production method disclosed herein. FIGS. 1B-1K areflow chart diagrams outlining the jig production method disclosedherein. The systems 4 for, and methods of, producing the customizedarthroplasty jigs 2 can be broken into six sections.

The first section, which is discussed with respect to FIG. 1A and[Blocks 100-115 and 125-135] of FIGS. 1B-1E, pertains to example methodsof generating two-dimensional (“2D”) body coil MRI images 52 and 2D kneecoil MRI images 16, identifying hip, knee and ankle center points 54,56, 57, 58 in the 2D body coil MRI images 52, and matching the 2D kneecoil MRI images 16 to the 2D body coil MRI images 52 with respect tolocation and orientation in a global coordinate system 63.

The second section, which is discussed with respect to FIG. 1A and[Blocks 140-170] of FIGS. 1E-1G, pertains to example methods ofpre-operative planning (“POP”) to determine bone resection locations andorientations in a knee arthroplasty. For example, the second sectionincludes establishing a reference point P in the 2D knee coil MRI images16, segmenting the 2D knee coil MRI images 16, generating 3D bone models22 from the segmented images, generating 3D restored bone models 28 fromthe bone models 22, shape matching the 3D restored bone models 28 to 3Dimplant models 34 in a 3D computer model environment, noting thelocation and orientation of saw cut (bone resection) and drill holelocations 30, 32, and adjusting for ligament balance.

The resulting “saw cut and drill hole data” 44 is referenced to therestored hone models 28 to provide saw cuts and drill holes that willallow arthroplasty implants to achieve a joint alignment that is: (1)generally representative of the patient's pre-degenerative joint line(i.e., natural alignment); generally corresponding to a zero mechanicalaxis alignment; or (3) somewhere between (1) and (2). Whether theresections result in a joint alignment that is (1), (2) or somewherebetween (1) and (2) may be a result of physician input and modificationof the natural joint alignment calculated during POP.

The third section, which is discussed with respect to [Blocks 190-235]of FIGS. 1H-1I, pertains to example methods of presenting information tothe surgeon regarding the POP and, more specifically, the resections 30,joint line 64, femoral mechanical axis (“FMA”) 68, tibial mechanicalaxis (“TMA”) 70, and mechanical axis (“MA”) 72. The surgeon providesapproval of the present POP information or directions to modify the POP.

The fourth section, which is discussed with respect to [Blocks 120, 175,180 and 255] of FIGS. 1C, 1G and 1J, pertains to examples of methods ofmaintaining location and orientation relationships between the various3D models 22, 28, 36 and center points 54, 56, 57, 58 as the various 3Dmodels 22, 28, 36 are modified or otherwise manipulated.

The fifth section, which is discussed with respect to FIG. 1A and[Blocks 180 and 245-260] of FIGS. 1E, 1G and 1J, pertains to examplemethods of generating 3D arthritic models 36 from the segmented images,importing into the 3D computer generated jig models 38 3D computergenerated surface models 40 of arthroplasty target areas 42 of the 3Dcomputer generated arthritic models 36 of the patient's joint bones, andupdating the location and orientation of the these models 36, 38, 40 tomaintain the location and position relationship with the bone models 22,28 that are manipulated during POP. The resulting “jig data” 46 is usedto produce a jig customized to matingly receive the arthroplasty targetareas of the respective bones of the patient's joint.

The sixth section, which is discussed with respect to FIG. 1A and[Blocks 240 and 265-285] of FIG. 1K, pertains to methods of combining orintegrating the “saw cut and drill hole data” 44 with the “jig data” 46to result in “integrated jig data” 48. The “integrated jig data” 48 isprovided to the CNC machine 10 or another automated production machine,such as, for example, a rapid production machine (e.g., astereolithography apparatus (“SLA”) machine) for the production ofcustomized arthroplasty jigs 2 from jig blanks 50 provided to the CNCmachine 10. The resulting customized arthroplasty jigs 2 include saw cutslots and drill holes positioned in the jigs 2 such that when the jigs 2matingly receive the arthroplasty target areas of the patient's bones,the cut slots and drill holes facilitate preparing the arthroplastytarget areas in a manner that allows the arthroplasty joint implants toachieve a predetermined or desired joint alignment. Depending on thephysician's review and input as outlined in [Blocks 190-235] of FIGS.1H-1I, the predetermined or desired joint alignment will: generallyrestore the patient's joint line to its pre-degenerated state or naturalalignment state; generally correspond to a zero degree mechanical axisalignment; or be somewhere between natural alignment and zero degreemechanical axis alignment.

As shown in FIG. 1A, the system 4 includes a computer 6 having a CPU 7,a monitor or screen 9 and operator interface controls 11. The computer 6is linked to a medical imaging system 8, such as a CT or MRI machine 8,and a computer controlled manufacturing system 10, such as a CNC millingmachine 10.

As indicated in FIG. 1A, a patient 12 has a hip joint 13, a knee joint14, and an ankle joint 15, wherein the knee joint 14 is to be thesubject of the arthroplasty procedure. In other embodiments, the joint14 to be replaced may be another type of joint, for example, an elbow,ankle, wrist, hip, shoulder, skull/vertebrae or vertebrae/vertebraeinterface, etc. As discussed in greater detail below, in one embodiment,the patient 12 has the hip, knee and ankle joints 13, 14, 15 scanned inthe imaging machine 8. The imaging machine 8 makes a plurality of scansof the joints 13, 14, 15 wherein each scan pertains to a thin slice of asingle joint or multiple joints.

As can be understood from FIG. 1B, in one embodiment, the patient's legbone structure undergoes two types of scanning in the imaging machine 8.Specifically, as indicated in FIG. 6, which is an isometric view of thepatient's leg bone structure, in one embodiment, the patient's knee 14,including portions of the femur 18 and tibia 20, is scanned in a MRIknee coil to generate a plurality of two dimensional (“2D)”) knee coilMRI images 16 of the patient's knee 14 [Block 100]. In one embodiment,the knee coil 2D images 16 include a plurality of coronal images 16 a, aplurality of axial images 16 b and a plurality of sagittal images 16 c.In other embodiments, the knee coil 2D images 16 may be any combinationof coronal, sagittal and/or axial views; for example, the views makingup the images 16 may be coronal plus sagittal, coronal plus sagittalplus axial, coronal plus axial, etc. The knee coil 2D images 16 have alocation and orientation in a global coordinate system 63 having anorigin (X0, Y0, Z0). In one embodiment, the MRI imaging spacing for the2D knee coil images 16 may range from approximately 2 mm toapproximately 6 mm.

As illustrated in FIG. 7, which is an isometric view of the patient'sleg bone structure, in one embodiment, the patient's entire leg length,or portions thereof that include the patient's hip 13, knee 14 and ankle15, is scanned in a MRI body coil to generate a plurality of 2D bodycoil MRI images 52 of the patient's entire leg length or, at least, aplurality of body coil 2D MRI images 52 at each of the patient's the hip13, knee 14 and ankle 15 [Block 105]. In other words, the body coil 2Dimages 52 include all of hip 13, knee 14 and ankle 15 or, at least,certain portions thereof. In one embodiment, the body coil 2D images 52include a plurality of coronal images 52 a, a plurality of axial images52 b and a plurality of sagittal images 52 c at each of the hip 13, knee14 and ankle 15. In other embodiments, the body coil 2D images 52 may beany combination of coronal, sagittal and/or axial views; for example,the views making up the images 52 may be coronal plus sagittal, coronalplus sagittal plus axial, coronal plus axial, etc. The body coil 2Dimages 52 have a location and orientation in the global coordinatesystem 63 having the origin (X0, Y0, Z0). In one embodiment, the MRIimaging spacing for the 2D body coil images 52 may range fromapproximately 0.5 mm to approximately 5 mm. As a result, the number ofgenerated MRI imaging slices for the knee coil approach is larger thanthe body coil approach. In other words, the numbers N for the knee coiland M for the body coil of MRI slices may be expressed as follows:N(coronal slices)>>M(coronal slices); N(sagittal slices)>>M(sagittalslices); and N(axial slices)>>M(axial slices).

As can be understood from FIG. 1B, in one embodiment, before performingthe MRI scanning that will result in the body coil 2D images 52, the MRIlocalizer may be employed in the sagittal and axial views of thepatient's leg bone structure to target the MRI scanning process at thecenters of the patient's hip 13, knee 14 and ankle 15 [Block 103]. Thus,the MRI body coil scanning may be caused to focus at the centers of thehip, knee and ankle, increasing the likelihood of generating coronalbody coil images that are adequate for identifying the centers of thehip, knee and ankle as discussed below.

While the embodiment is discussed in the context of the imaging beingvia MRI, in other embodiments the imaging is via CT or other medicalimaging methods and systems. In one embodiment employing MRI, theimaging process may be as disclosed in U.S. patent application Ser. No.11/946,002 to Park, which is titled “Generating MRI Images Usable ForThe Creation Of 3D Bone Models Employed To Make Customized ArthroplastyJigs,” was filed Nov. 27, 2007 and is incorporated by reference in itsentirety into this Detailed Description.

As can be understood from FIG. 1A, the 2D images 16, 52 are sent to thecomputer 6 for analysis and modeling. As indicated in FIG. 1C, hip, kneeand ankle centers 54, 56, 57, 58 are identified in the body coil 2Dimages 52 [Block 110]. For example, as indicated FIGS. 14-16, which arecoronal 2D body coil images 52 of the hip 13, knee 15 and ankle 16,respectively, a person sitting in front of the monitor 9 of the workstation 6 tabs through the various coronal 2D body coil images 52 ateach of the hip, knee and ankle to determine visually an image 52 ateach of the hip, knee and ankle that is near the center of each of thesejoints 13, 14, 15. When the operator visually identifies such an imagefor each of the joints 13, 14, 15, the operator electronically marks thecenters 54, 56, 57, 58 for each of these joints 13, 14, 15, as indicatedin FIGS. 14-16, causing the location of the centers 54, 56, 57, 58 to beelectronically stored relative to the global coordinate system 63.

In one embodiment, the hip, knee and ankle centers 54, 56, 57, 58 areidentified only in the coronal views of the body coil 2d images 52. Inone embodiment, the X, Y and Z global coordinate locations for each ofthe femur hip center 54, femur knee center 56, tibia knee center 57 andtibia ankle center 58 are stored, for example, in a table or matrix in acomputer file separate from the 3D bone models 22 or 3D restored bonemodels 28, discussed below [Block 115]. In other embodiments, the X, Yand Z global coordinate locations for each of the femur hip center 54,femur knee center 56, tibia knee center 57 and tibia ankle center 58 arestored with or as part of the 3D bone models 22 or 3D restored bonemodels 28, discussed below.

In one embodiment, the hip center can be the approximate center point ofthe femur head via visual examination. The ankle center can be theapproximate center point of the cortical bone rim of the ankle plafond(i.e., the distal articular surface of tibia) via visual examination.The knee center can be the approximate center point close to theintercondylar groove of the distal femur and/or the approximate centerpoint of the tibia spine in the 3D restored knee model. The centers ofthe hip and ankle in the 2D body coil images 52 may be identified. Theapproximate joint center coordinates of the hip, ankle and 3D knee modelmay be recorded as (x′1-3, y′1-3, z′1-3). For example, the joint centercoordinates for each of hip, knee, and ankle, may be, respectively,(x′1, y′1, z′1), (x′2, y′2, z′2), and (x′3, y′3, z′3).

As shown in FIG. 1D, points 60 and 62 are identified respectively oncorresponding landmarks in the 2D body coil images 52 and 2D knee coilimages 16 [Block 125]. For example, as shown in FIG. 8, which is acoronal 2D knee coil image 16, points 62 are identified on landmarks ofthe knee region of the femur 18. In some embodiments, the 2D knee coilimage 16 used to identify the landmarks of the knee region of the femur18 is the 2D knee coil image 16 of the set of knee coil images 16 havingthe widest and most clear or definite depiction of the femur 18 in theknee region. For example, a person viewing the 2D knee coil images 16via the monitor 9 of the work station 6 may tab through the variouscoronal 2D knee coil images 16 to determine the specific coronal 2D kneecoil image 16 in which the femur 18 is depicted with the largest andmost clear condyle contour. The person then marks or identifies thepoints 62 of the femur landmarks. As shown in FIG. 8, examples of suchlandmarks on the knee region of the femur may include the center of thefemur condyle region near the trochlear groove, the most medial andlateral points of the epicondyles, or other identifiable landmarks.

As shown in FIG. 9, which is a coronal 2D knee coil image 16, points 62may also be identified on landmarks of the knee region of the tibia 20.In some embodiments, the 2D knee coil image 16 used to identify thelandmarks of the knee region of the tibia 20 is the 2D knee coil image16 of the set of knee coil images 16 having the widest and most clear ordefinite depiction of the tibia 20 in the knee region. For example, aperson viewing the 2D knee coil images 16 via the monitor 9 of the workstation 6 may tab through the various coronal 2D knee coil images 16 todetermine the specific coronal 2D knee coil image 16 in which the tibia20 is depicted with the largest and most clear condyle contour. Theperson then marks or identifies the points 62 of the tibia landmarks. Asshown in FIG. 9, examples of such landmarks on the knee region of thetibia may include the medial and lateral edges of the tibial condyles,the medial and lateral transitions from the tibial plateau to the tibialshaft, or other identifiable landmarks.

As shown in FIG. 10, which is a coronal 2D body coil image 52, points 60are identified on landmarks of the knee region of the femur 18. In someembodiments, the 2D body coil image 52 used to identify the landmarks ofthe knee region of the femur 18 is the 2D body coil image 52 of the setof body coil images 52 having the widest and most clear or definitedepiction of the femur 18 in the knee region. For example, a personviewing the 2D body coil images 52 via the monitor 9 of the work station6 may tab through the various coronal 2D body coil images 52 todetermine the specific coronal 2D body coil image 52 in which the femur18 is depicted with the largest and most clear condyle contour. Theperson then marks or identifies the points 60 of the femur landmarks,which, as can be understood from a comparison of FIGS. 10 and 8, will beselected to be at least generally the same as the points 62 of the femurlandmarks identified in the coronal 2D knee coil image 16.

As shown in FIG. 11, which is a coronal 2D body coil image 52, points 60are also identified on landmarks of the knee region of the tibia 20. Insome embodiments, the 2D body coil image 52 used to identify thelandmarks of the knee region of the tibia 20 is the 2D body coil image52 of the set of body coil images 52 having the widest and most clear ordefinite depiction of the tibia 20 in the knee region. For example, aperson viewing the 2D body coil images 52 via the monitor 9 of the workstation 6 may tab through the various coronal 2D body coil images 52 todetermine the specific coronal 2D body coil image 52 in which the tibia20 is depicted with the largest and most clear condyle contour. Theperson then marks or identifies the points 60 of the tibia landmarks,which, as can be understood from a comparison of FIGS. 11 and 9, will beselected to be at least generally the same as the points 62 of the tibialandmarks identified in the coronal 2D knee coil image 16.

In one embodiment, three or more points 62 are identified in therespective 2D knee coil images 16 of FIGS. 8 and 9, and three or morepoints 60 are identified in the respective 2D body coil images 52 ofFIGS. 10 and 11. The three or more femur points 62 may be in the samecoronal 2D knee coil image 16, as illustrated in FIG. 8, and the threeor more tibia points 62 may be in the same coronal 2D knee coil image16, as depicted in FIG. 9. Similarly, the three or more femur points 60may be in the same coronal 2D body coil image 52, as illustrated in FIG.10, and the three or more tibia points 60 may be in the same coronal 2Dbody coil image 52, as depicted in FIG. 11.

In other embodiments, the three or more points 60, 62 may be distributedacross multiple coronal images 16, 52. For example, the three or morefemur points 62 may be distributed across two or more coronal 2D kneecoil images 16, and the three or more tibia points 62 may be distributedacross two or more coronal 2D knee coil images 16. Similarly, the threeor more femur points 60 may be distributed across two or more coronal 2Dbody coil images 52, and the three or more tibia points 60 may bedistributed across two or more coronal 2D body coil images 52.

In yet other embodiments, the three or more points 60, 62 may bedistributed across different types of images 16, 52, such as, forexample, a combination of coronal, axial and/or sagittal. For example,the three or more femur points 62 may be distributed across one or morecoronal 2D knee coil image 16, one or more sagittal knee coil image,and/or one or more axial knee coil image, and the three or more tibiapoints 62 may be distributed across one or more coronal 2D knee coilimage 16, one or more sagittal knee coil image, and/or one or more axialknee coil image. Similarly, the three or more femur points 60 may bedistributed across one or more coronal 2D body coil image 52, one ormore sagittal body coil image, and/or one or more axial body coil image,and the three or more tibia points 60 may be distributed across one ormore coronal 2D body coil image 52, one or more sagittal body coilimage, and/or one or more axial body coil image.

Regardless of how many points 60, 62 are located and in which type ofimage views and combinations of views, in one embodiment, the coordinatelocations of the points 60, 62 in the global coordinate system 63 arestored for use with the transformation process discussed below.

As can be understood from FIG. 1D, the 2D knee coil images 16 are movedto the location of the 2D body coil images 52 in the global coordinatesystem 63, or vice versa [Block 130]. As can be understood from FIG. 1E,a transformation is run for the points 60, 62 to cause the 2D knee coilimages 16 to generally positionally match the 2D body coil images 52with respect to both location and orientation [Block 135]. Specifically,as can be understood from FIG. 12, which is a diagrammatic depiction ofthe femur images 16, 52 being transformed, the transformation, in oneembodiment, causes the coronal 2D knee coil images 16 a to move to andpositionally match the coronal 2D body coil images 52 a by positioningthe points 62 of the coronal 2D knee coil images 16 a at the positionsof the corresponding points 60 of the coronal 2D body coil images 52 ain the global coordinate system 63. The embodiment of the transformationalso causes the axial 2D knee coil images 16 b to move to andpositionally match the axial 2D body coil images 52 b by positioning thepoints 62 of the axial 2D knee coil images 16 b at the positions of thecorresponding points 60 of the axial 2D body coil images 52 b in theglobal coordinate system 63. The embodiment of the transformation alsocauses the sagittal 2D knee coil images 16 c to move to and positionallymatch the sagittal 2D body coil images 52 c by positioning the points 62of the sagittal 2D knee coil images 16 c at the positions of thecorresponding points 60 of the sagittal 2D body coil images 52 c in theglobal coordinate system 63.

As can be understood from FIG. 13, which is a diagrammatic depiction ofthe tibia images 16, 52 being transformed, the transformation, in oneembodiment, causes the coronal 2D knee coil images 16 a to move to andpositionally match the coronal 2D body coil images 52 a by positioningthe points 62 of the coronal 2D knee coil images 16 a at the positionsof the corresponding points 60 of the coronal 2D body coil images 52 ain the global coordinate system 63. The embodiment of the transformationalso causes the axial 2D knee coil images 16 b to move to andpositionally match the axial 2D body coil images 52 b by positioning thepoints 62 of the axial 2D knee coil images 16 b at the positions of thecorresponding points 60 of the axial 2D body coil images 52 b in theglobal coordinate system 63. The embodiment of the transformation alsocauses the sagittal 2D knee coil images 16 c to move to and positionallymatch the sagittal 2D body coil images 52 c by positioning the points 62of the sagittal 2D knee coil images 16 c at the positions of thecorresponding points 60 of the sagittal 2D body coil images 52 c in theglobal coordinate system 63.

Whether the transformation operates on points in a particular view(e.g., coronal, axial and/or sagittal) or on a particular bone (e.g.,femur and/or tibia) will depend on which landmarks the points 60, 62 areidentified and in which views, as discussed above with respect to [Block125] of FIG. 1D.

In one embodiment, the MRI coordinates of the points 60 on the bonelandmarks of the region of the knee 14 in the 2D body coil images 52 maybe illustrated as (x, y, z) and stored for further analysis. Similarly,the MRI coordinates of the points 62 on the bone landmarks of the regionof the knee 14 in the 2D knee coil images 16 may be illustrated as({circumflex over ( )}x, {circumflex over ( )}y, {circumflex over ( )}z)and stored for further analysis. In one embodiment, the landmarks onwhich the points 60, 62 are located may be the epicondylar points of thedistal femur, the approximate center of distal femur, the approximatecenter of proximal tibia, or other recognizable landmarks. In anotherembodiment, the points 60, 62 can be located anywhere on the area ofdistal femur and proximal tibia. The points for both the knee coilimages 16 and body coil images 52 are in approximately similar locationsvia visual examination.

Once the points 60, 62 are similarly located in the images 16, 52, thetransformation or optimization of the points 60, 62 and associatedimages 16, 52 takes place by brining as close as possible the points 62of the 2D knee coil images 16, which are stored as ({circumflex over( )}x, {circumflex over ( )}y, {circumflex over ( )}z), to the points ofthe 2D body coil images 52, which are stored as (x, y, z). In otherwords, for example, the closeness of the two sets of points may beevaluated as the sum of squared distances from points in the first setto the whole second set. The manipulations of rotation and translationare applied to the points and associated images for the distal femur andproximal tibia.

In one embodiment, the transformation employs the Iterative ClosestPoint (“ICP”) algorithm, gradient descent optimization or otheroptimization algorithms or transformations.

While [Blocks 125-135] of FIGS. 1D-1E and the preceding discussionillustrate a first positional matching embodiment wherein the 2D kneecoil images 16 are positionally matched to the 2D body coil images 52via the positional matching of landmark points 60, 62, other embodimentsmay employ other positional matching methods. For example, in a secondpositional matching embodiment and in a manner similar to that discussedbelow with respect to [Blocks 145-150] of FIGS. 1E-1F, the 2D knee coilimages 16 are segmented and converted into a 3D bone model 22. Landmarkpoints 60 are identified in the 2D body coil images 52 and theselandmark points 60 are positionally matched to corresponding landmarkpoints 62 in the 3D bone model 22 via the ICP.

A third positional matching embodiment employs a contour to contourpositional matching approach. In one version of the third positionalmatching embodiment, splines are defined along the bone contours in the2D body coil images 52 and along the bone contours in the 2D knee coilimages 16. In another version of the third positional matchingembodiment, the 2D knee coil images 16 are segmented and converted intoa 3D bone model 22, and splines are defined along the bone contours inthe 2D body coil images 52.

In some versions of the third positional matching embodiment, thesplines are generally limited to the bone contours at specificlandmarks. In other versions of the third positional matchingembodiment, the splines extend along a substantial portion, if not theentirety, of the bone contours. Regardless of which version of the thirdpositional matching embodiment is employed, the splines of the bonecontours of the 2D body coil images 52 are positionally matched to bonecontours of the 2D knee coil images 16 or the descendent 3D bone model22 via the ICP algorithm or one of the other above-mentionedtransformations. In one version of the third positional matchingembodiment, the contours employed exist in both coronal and sagittalimage slices.

In a fourth positional matching embodiment, image intensity variationsin the 2D knee coil images 16 are identified and positionally matched tocorresponding image intensity variations identified in the 2D body coilimages 52. For example, image registration techniques are employed thatare similar to those described in U.S. patent application Ser. No.12/386,105, which was filed Apr. 4, 2009, titled System and Method forImage Segmentation in Generating Computer Models of a Joint to UndergoArthroplasty, and is hereby incorporated by reference into the presentapplication in its entirety. Specifically, a bone 18, 20 in the 2D kneecoil images 16 is segmented by a technician. Additionally, a technicianmay provide an initial approximate transform by specifying one or morelandmarks in each of the knee coil and body coil images. The group ofthe rigid 3D transform with 6 parameters P (3 rotational angle+3translation parameters) is parameterized. The function to be optimizedis defined (see application Ser. No. 12/386,105—local image correlationfunction F). In one version of the fourth positional matchingembodiment, a set of points S is defined in the knee coil images to beused in function F (e.g., the set of points S might be all the voxelpoints within 3-5 mm distance from the segmentation contours or somesubset of such voxel points (e.g., a random subsample of such voxelpoints)). For every 6-dimensional parameter p in P, transform T(p) isapplied to the set S to compute correlation F in the transformed setf(p)=F(T(p)(S)). Standard optimization techniques are applied in orderto maximize f over parameters p. For example, when a technician providesan initial approximate transform, a gradient descent optimization methodmay be employed.

As can be understood from the preceding discussion, the variouspositional matching embodiments may employ a rigid 3D transform thatbest aligns the femur 18 in the 2D knee coil images 16 to the femur 18in the 2D body coil images 52. A similar rigid 3D transform may also beemployed in the various positional matching embodiments to best alignthe tibia 20 in the 2D knee coil images 16 to the tibia 20 in the 2Dbody coil images 52.

A given transform can be applied to the images 16, 52. In other words, afirst image can be resampled over the transform. The transformed firstimage can be overlapped with the second image with the goal of thetransform being that the two overlapped images match as close aspossible in the region of femur bone. The transform process can besimilarly run for the tibia.

While, in some embodiments, the transformed knee coil images and thebody coil images may not match precisely because every MRI has a numberof its own artifacts that degrade the image differently in differentareas, the positional matching will be sufficient to allow the rest ofthe POP to continue as described herein.

As a general summary, in one embodiment, a few distinguished landmarksin the knee coil images are positional matched to similar orcorresponding landmarks in the body coil images. In another embodiment,a larger number of points on the bone boundary in the body coil imagesare matched to the whole bone boundary (e.g., to the mesh surface in 3D)in the knee coil images. In yet another embodiment, the contours on thebone boundary in the body coil images are matched to the whole boundaryof the knee coil images or, alternatively, the descendent 3D bone model.In the yet another embodiment, the image intensity variations around thebone boundary in the body coil images are matched to the image intensityvariations in the knee coil images.

Each of embodiments one through three of the positional matching methodmay be done via a combination of manual and automated methodology or viaan entirely automated methodology. The fourth embodiment of thepositional matching method may be entirely automated.

As indicated in FIG. 1E, in one embodiment, point P is identified in the2D knee coil images 16 once the 2D knee coil images 16 are positionallymatched to the 2D body coil images 52 [Block 140]. In one embodiment,point P may be at the approximate medial-lateral and anterior-posteriorcenter of the patient's knee joint 14. In other embodiments, point P maybe at any other location in the 2D knee coil images 16, includinganywhere on, near or away from the bones 18, 20 or the joint 14 formedby the bones 18, 20.

As described below with respect to [Blocks 180 and 255] of FIGS. 1G and1J, respectively, point P may be used to locate the computer generated3D models 22, 28, 36 created from the 2D knee coil images 16 and tointegrate information generated via the 3D models. Depending on theembodiment, point P, which serves as a position and/or orientationreference, may be a single point, two points, three points, a point plusa plane, a vector, etc., so long as the reference P can be used toposition and/or orient the 3D models 22, 28, 36 generated via the 2Dknee images 16.

As indicated in FIG. 1E, the 2D knee coil images 16 are segmented alongthe bone surface boundaries to generate 2D bone-only contour lines[Block 145]. The 2D knee coil images 16 are also segmented alongcartilage and bone surface boundaries to generate 2D bone and cartilagecontour lines [Block 245]. In one embodiment, the bone surface contourlines and cartilage-and-bone surface contour lines of the bones 18, 20depicted in the 2D knee coil image slices 16 may be auto segmented viaan image segmentation process as disclosed in U.S. patent applicationSer. No. 12/386,105, which was filed Apr. 4, 2009, is titled System andMethod for Image Segmentation in Generating Computer Models of a Jointto Undergo Arthroplasty, and is hereby incorporated by reference intothe present application in its entirety.

As can be understood from FIG. 1F, the 2D bone-only contour linessegmented from the 2D knee coil images 16 are employed to createcomputer generated 3D bone-only (i.e., “bone models”) 22 of the bones18, 20 forming the patient's knee 14 [Block 150]. The bone models 22 arelocated such that point P is at coordinates (X0-j, Y0-j, Z0-j) relativeto an origin (X0, Y0, Z0) of the global coordinate system 63. In oneembodiment, the bone models 22 incorporate the hip, knee and anklecenters 54, 56, 57, 58, and these centers 54, 56, 58 are positioned soas to reflect their correct respective locations with respect to theorientation and location of the bone models 22. In another embodiment,the hip, knee and ankle centers 54, 56, 57, 58 are not incorporated intothe bone models 22, but are linked to the bone models 22 such that thehip, knee and ankle centers 54, 56, 57, 58 may be toggled on or off todisplay with the bone models 22 or be hidden. In such an embodiment, thehip, knee and ankle centers 54, 56, 57, 58 are positioned so as toreflect their correct respective locations with respect to theorientation and location of the bone models 22 when the centers 54, 56,57, 58 are toggled on to be visible with the bone models 22.

Regardless of whether the centers 54, 56, 57, 58 are part of the bonemodels 22 or separate from the bone models 22 but capable of being shownwith the bone models 22, the bone models 22 depict the bones 18, 20 inthe present deteriorated condition with their respective degeneratedjoint surfaces 24, 26, which may be a result of osteoarthritis, injury,a combination thereof, etc. Also, the hip, knee and ankle centers 54,56, 57, 58 and bone surfaces 24, 26 are positioned relative to eachother as would generally be the case with the patient's long leg anatomyin the present deteriorated state. That the centers 54, 56, 57, 58 arecorrectly oriented with respect to the bone models 22 to represent thepatient's long leg anatomy in the present deteriorated state is madepossible, at least in part, via the transformation process describedabove with respect to [Blocks 125-135] of FIGS. 1D-1E and FIGS. 8-13.

In one embodiment, the systems and methods disclosed herein create the3D computer generated bone models 22 from the bone-only contour linessegmented from the 2D knee coil images 16 via the systems and methodsdescribed in U.S. patent application Ser. No. 12/386,105, which wasfiled Apr. 4, 2009, is entitled System and Method for Image Segmentationin Generating Computer Models of a Joint to Undergo Arthroplasty, and ishereby incorporated by reference into the present application in itsentirety. In other embodiments the systems and methods disclosed hereinemploy any one or more of the following computer programs to create the3D computer generated bone models 22 from the bone-only contour linessegmented from the 2D knee coil images 16: Analyze from AnalyzeDirect,Inc., Overland Park, Kans.; Insight Toolkit, an open-source softwareavailable from the National Library of Medicine Insight Segmentation andRegistration Toolkit (“ITK”), www.itk.org; 3D Slicer, an open-sourcesoftware available from www.slicer.org; Mimics from Materialise. AnnArbor, Mich.; and Paraview available at www.paraview.org.

As indicated in FIG. 1F, the 3D computer generated bone models 22, orassociated bone-only contour lines, are utilized to create 3D computergenerated “restored bone models” or “planning bone models” 28 whereinthe degenerated surfaces 24, 26 are modified or restored toapproximately their respective conditions prior to degeneration [Block155]. Thus, the bones 18, of the restored bone models 28 and theirrespective restored bone surfaces 24′, 26′ are reflected inapproximately their condition prior to degeneration. The restored bonemodels 28 are located such that point P is at coordinates (X0-j, Y0-j,Z0-j) relative to the origin (X0, Y0, Z0) of the global coordinatesystem 63. Thus, the restored bone models 28 share the same orientationand positioning relative to the origin (X0, Y0, Z0) of the globalcoordinate system 63 as the bone models 22.

As with the bone models 22 discussed above, the hip, knee and anklecenters 54, 56, 57, 58 may be incorporated into the restored bone models28 or stored separately from the restored bone models 28, but capable ofbeing toggled on or off to be displayed relative to the restored bonemodels 28 or hidden.

In one embodiment, the restored bone models 28 are manually created fromthe bone models 22 by a person sitting in front of a computer 6 andvisually observing the bone models 22 and their degenerated surfaces 24,26 as 3D computer models on a computer screen 9. The person visuallyobserves the degenerated surfaces 24, 26 to determine how and to whatextent the degenerated surfaces 24, 26 surfaces on the 3D computer bonemodels 22 need to be modified to restore them to their pre-degeneratedcondition. By interacting with the computer controls 11, the person thenmanually manipulates the 3D degenerated surfaces 24, 26 via the 3Dmodeling computer program to restore the surfaces 24, 26 to a state theperson believes to represent the pre-degenerated condition. The resultof this manual restoration process is the computer generated 3D restoredbone models 28, wherein the surfaces 24′, 26′ are indicated in anon-degenerated state.

In one embodiment, the above-described bone restoration process isgenerally or completely automated, as disclosed in U.S. patentapplication Ser. No. 12/111,924 to Park, which is titled Generation of aComputerized Bone Model Representative of a Pre-Degenerated State andUsable in the Design and Manufacture of Arthroplasty Devices, was filedApr. 29, 2008 and is incorporated by reference in its entirety into thisDetailed Description. In other words, a computer program may analyze thebone models 22 and their degenerated surfaces 24, 26 to determine howand to what extent the degenerated surfaces 24, 26 surfaces on the 3Dcomputer bone models 22 need to be modified to restore them to theirpre-degenerated condition. The computer program then manipulates the 3Ddegenerated surfaces 24, 26 to restore the surfaces 24, 26 to a stateintended to represent the pre-degenerated condition. The result of thisautomated restoration process is the computer generated 3D restored bonemodels 28, wherein the surfaces 24′, 26′ are indicated in anon-degenerated state.

As depicted in FIG. 1F, once the restored bone models 28 have beengenerated as discussed above with respect to [Block 155], the restoredbone models 28 are employed in a pre-operative planning (“POP”)procedure to determine saw cut (bone resection) locations 30 and drillhole locations 32 in the patient's bones that will allow thearthroplasty joint implants to generally restore the patient's jointline to its pre-degenerative alignment. Specifically, the POP processbegins by moving the restored bone models 28 to the location of 3Dmodels 34 of arthroplasty implant models proposed for use in the actualarthroplasty procedure [Block 160]. In moving the restored bone models28 to the implant models 34, point p on the restored bone models 28moves from coordinates (X0-j, Y0-j, Z0-j) to coordinates (X0-k, Y0-k,Z0-k) and becoming point P′. The implant models 34 include planarsurfaces representative of the planar surfaces of the actual implantsthat intersect resected bone surfaces. These planar surfaces of theimplant models 34 are used to determine resection or saw cut locations30 during the POP. Also, the implant models 34 include screw holesrepresentative of the screw holes of the actual implants that hold bonescrews for retaining the actual implant in place on the resected bone.These holes of the implant models 34 are used to determine drill holelocations 32 during POP.

In one embodiment, the POP procedure is a manual process, whereincomputer generated 3D implant models 34 (e.g., femur and tibia implantsin the context of the joint being a knee) and restored bone models 28are manually manipulated relative to each other by a person sitting infront of a computer 6 and visually observing the implant models 34 andrestored bone models 28 on the computer screen 9 and manipulating themodels 28, 34 via the computer controls 11. As can be understood fromFIG. 1G, by superimposing the implant models 34 over the restored bonemodels 28, or vice versa, the joint surfaces of the implant models 34can be aligned, shape fit, or otherwise caused to correspond with thejoint surfaces of the restored bone models 28 [Block 165]. By causingthe joint surfaces of the models 28, 34 to so align, the implant models34 are positioned relative to the restored bone models 28 such that thesaw cut locations 30 and drill hole locations 32 can be determinedrelative to the restored bone models 28.

In one embodiment, the POP process is generally or completely automated.In one embodiment, the above-described POP process is generally orcompletely automated, as disclosed in U.S. patent application Ser. No.12/563,809 to Park, which is titled Arthroplasty System and RelatedMethods, was filed Sep. 21, 2009 and is incorporated by reference in itsentirety into this Detailed Description. In other words, a computerprogram may manipulate computer generated 3D implant models 34 (e.g.,femur and tibia implants in the context of the joint being a knee) andrestored bone models or planning bone models 28 relative to each otherto determine the saw cut and drill hole locations 30, 32 relative to therestored bone models 28. The implant models 34 may be superimposed overthe restored bone models 28, or vice versa. In one embodiment, theimplant models 34 are located at point P′ (X0-k, Y0-k, Z0-k) relative tothe origin (X0, Y0, Z0) of the global coordinate system 63, and therestored bone models 28 are located at point P (X0-j, Y0-j, Z0-j). Tocause the joint surfaces of the models 28, 34 to correspond, thecomputer program may move the restored bone models 28 from point P(X0-j, Y0-j, Z0-j) to point P′ (X0-k, Y0-k, Z0-k), or vice versa [Block160]. Once the joint surfaces of the models 28, 34 are in closeproximity, the joint surfaces of the implant models 34 may beshape-matched to align or correspond with the joint surfaces of therestored bone models 28 [Block 165]. By causing the joint surfaces ofthe models 28, 34 to so align, the implant models 34 are positionedrelative to the restored bone models 28 such that the saw cut locations30 and drill hole locations 32 can be determined relative to therestored bone models 28. As a result of this POP process, the resectionlocations 30 will be such that the actual implants will generallyrestore the patient's knee geometry to what it was prior todegeneration.

As depicted in FIG. 1G, in one embodiment, a joint gap analysis isconducted to adjust orientation of the restored bone models 28 andarthroplasty implant models 34 so the joint gap on each side of joint isgenerally equal, causing the joint line 64 to be generally parallel tofloor and generally representative of the patient's pre-degenerativejoint line 64 [Block 170]. Further detail regarding the joint gapanalysis is provided in U.S. patent application Ser. No. 12/563,809 toPark, which is titled Arthroplasty System and Related Methods, was filedSep. 21, 2009 and is incorporated by reference in its entirety into thisDetailed Description.

As indicated in FIG. 1G, once the POP process is completed, adetermination is made regarding the 3D location and/or orientationimpact on the hip, knee and ankle center points 54, 56, 57, 58 onaccount of any of the processes of [Blocks 160, 165 & 170] or any otherposition and/or orientation change to the bone models 22 or restoredbone models 28 [Block 175]. As discussed above with respect to [Block135] of FIG. 1E, the location and orientation relationships between thehip, knee and ankle centers 54, 56, 57, 58 and the knee coil 2D images16 are established. These location and orientation relationships betweenthe hip, knee and ankle centers 54, 56, 57, 58 and the knee coil 2Dimages 16 and the descendant 3D bone models 22, 28 of the knee coil 2Dimages 16 are maintained throughout the various processes describedherein. Thus, as indicated in FIG. 1C, the X, Y and Z global coordinatelocations and/or orientations of each of the center points 54, 56, 57,58 in “Table A” of [Block 115] are updated for any 3D location and/ororientation impact on the center points 54, 56, 57, 58 on account of anyof the processes of [Blocks 160, 165 & 170] or any other location and/ororientation change to the 3D bone models 22 or restored bone models 28[Block 120].

For example, after the joint gap analysis and manipulation is completeas recited in [Block 170], the coordinates for the joint centers of therestored 3D knee model are changed from (x′2, y′2, z′2) because of themanipulation of the models 28, 34 in bringing the joint line parallel tothe ground. After completion of the joint gap analysis and manipulation,the joint line 64 is set up and is perpendicular to the center of distalfemur and perpendicular to the center of proximal tibia. Suchmanipulation can be done for both the distal femur and proximal tibia.As a result, the coordinates of the joint centers of this newly aligned3D knee model (with joint line references and joint center points) maybe further identified and recorded as (x″2, y″2, z″2).

As indicated in FIG. 1G, once the POP process is completed, adetermination is made regarding the change in the 3D location and/ororientation of the bone models 22 or restored bone models 28 on accountof any of the processes of [blocks 160, 165, 170] or any other locationand/or orientation change to the bone models 22 or restored bone models28 [Block 180]. Such a determination is employed to update the locationand orientation of the arthritic models 36, as discussed below in [Block255] of FIG. 1J.

As illustrated in FIG. 1H, the hip, knee and ankle center points 54, 56,57, 58 and femoral mechanical axis 68, tibial mechanical axis 70, andmechanical axis 72 are depicted in 3D with the 3D restored bone models28 and 3D implant models 34 [Block 190]. This may be achieved where thecenter points 54, 56, 57, 58 are part of the 3D restored bone models 28or the center points are separate from the restored bone models 28, butcapable of being toggled on to be viewable in 3D with the restored bonemodels 28. The points 54, 56, 57, 58, axes 68, 70, 72, and models 28, 34are presented in a coronal view [Block 190]. By employing the restoredbone models 28 in the POP process and maintaining the proper locationand orientation of the hip, knee and ankle centers 54, 56, 57, 58 duringthe POP process, the models 28, 34 and centers 54, 56, 57, 58 illustratea general approximation of the patient's knee geometry prior todeterioration, both respect to the joint line 64 and the various axes 68m, 70, 72.

In one embodiment, a 2D coronal snapshot 69′ of the models 28, 34,points 54, 56, 57, 58, and axes 68, 70, 72 is created [Block 195]. Anexample of such a coronal snapshot 69′ is depicted in FIG. 17. Also, inone embodiment, a 2D coronal snapshot 69″ of the models 28, points 54,56, 57, 58, and axes 68, 70, 72, less the implant models 34, is created[Block 200]. Each of these snapshots 69′, 69″ depict the patient's jointgeometry in natural alignment or, in other words, as the patient's jointgeometry is believed to have generally existed prior to degeneration.

FIG. 18 is another version of the 2D coronal snapshot 69″′ that may beprovided to the physician, and FIG. 19 is a diagrammatic depiction ofthe axes 68, 70, 72 and their relationship to each other in the globalcoordinate system 63. The snapshot 69″′, which illustrates the naturalalignment knee geometry and depicts the varus/valgus (“v/v”)measurement, may be employed by the physician to determine the amount ofcorrection needed to bring the knee geometry to a neutral geometry or ageometry between natural and neutral the physician considers desirable.

As shown in FIGS. 18 and 19, the v/v angle θ for the femur 18 ismeasured between the FMA 68 and MA 72. The FMA 68 is a line extendingbetween the center of the femoral head to the center of the knee regionof the femur 18. The v/v angle φ for the tibia 20 is measured betweenthe TMA 70 and the MA 72. The TMA 70 is a line extending between thecenter of the ankle to the center of the knee region of the tibia 20.The MA 72 is a line extending between the center of the femoral head tothe center of the ankle. When the knee geometry is in a zero degreemechanical axis or neutral geometry, the FMA 68, TMA 70 and MA 72 willbe generally coextensively aligned with each other.

In one embodiment, if the v/v angles fall into an acceptable rangewherein θ, φ<±3°, then the snapshot 69″′ has an acceptable naturalgeometry and can be forwarded to the physician. If the v/v angles do notfall into an acceptable range wherein θ, φ<±3°, then the POP process isrun again to arrive at a natural geometry that is acceptable.

As shown in FIGS. 18 and 19, the angle X approximately equal to the sumof angles θ and φ.

As indicated in FIG. 1I, in one embodiment, one more of the 2D coronalsnapshots 69′, 69″, 69″′ are provided to the physician for review [Block205]. The physician reviews the proposed correction and associatednatural alignment depicted in the received snapshot(s) 69′, 69″, 69″′and provides feedback regarding the proposed correction [Block 210]. Ifthe physician approves of the proposed correction and associated naturalalignment depicted in the received snapshot(s) 69′, 69″, 69″′ [Block215], then the proposed correction is left as is [Block 235].

However, as can be understood from FIG. 1I, if the physician disapprovesof the proposed correction and associated natural alignment depicted inthe received snapshot(s) 69′, 69″ [Block 215], then the proposedcorrection and associated natural alignment is adjusted in the X-Y(coronal) plane according to physician input [Block 225], the adjustmentbeing made to the saw cut and drill hole locations 30, 32 of the 3Dmodels 28, 34 of [Block 170]. In other words, the proposed correctionand associated natural alignment is adjusted to a new proposedcorrection, wherein the new proposed correction is associated with azero degree mechanical axis (neutral) alignment or an alignmentsomewhere between the originally proposed natural alignment and aneutral alignment.

As can be understood from FIG. 20, which is a diagrammatic depiction ofa process of adjusting resection lines based on joint geometryinformation conveyed via the 2D coronal snapshots 69′, 69″, 69″′, theknee joint geometry is depicted in natural alignment at X, the jointline 64 being generally parallel to the ground and the FMA 68 and TMA 70being angled relative to the MA 72. Upon review, the physician maydetermine the resection lines 30 in image X should be adjusted to be asindicated in images Y to cause the knee joint geometry to assume analignment that is closer to neutral. As shown in image Z, where theresection lines 30 have been adjusted per the physician's direction andthe bones 18, 20 realigned, the joint line 64 is generally parallel tothe floor and the FMA 68 and TMA 70 are generally parallel to the MA 72,which is shown off of the bones 18, 20 for clarity purposes.

Thus, in summary of the events at [Block 215] of FIG. 1I, the physicianmay determine that the natural alignment is desirable and, as a result,the alignment of the restored bone model 28 is not changed [Block 235],or the physician may determine that the restored bone model 28 should berealigned from natural alignment to an alignment that is closer to zerodegree mechanical axis [Block 225].

If the alignment is updated as in [Block 225], then per [Block 230], the2D coronal snapshots 69′, 69″ of [Blocks 195 and 200] are regeneratedoff of the models 28, 34 of [Block 170] as updated per [Block 225]. Theupdated coronal snapshots 69′, 69″ are again sent to the physician[Block 205] and the process repeats itself as recited above with respectto [Blocks 210-230], until the physician agrees with the proposedcorrection [Block 215] and the proposed correction is found to bedesirable, no further correction being deemed necessary by the physician[Block 235].

As indicated in FIG. 1K, in one embodiment, the data 44 regarding thesaw cut and drill hole locations 30, 32 relative to point P′ (X0-k,Y0-k, Z0-k) is packaged or consolidated as the “saw cut and drill holedata” 44 [Block 240]. The “saw cut and drill hole data” 44 is then usedas discussed below with respect to [Block 270] in FIG. 1K.

As mentioned above with respect to FIG. 1E, the 2D knee coil images 16are segmented along cartilage and bone boundaries to generate 2D boneand cartilage contour lines [Block 245]. As can be understood from FIG.1J, the bone and cartilage contour lines are used to create computergenerated 3D bone and cartilage models (i.e., “arthritic models”) 36 ofthe bones 18, 20 forming the patient's joint 14 [Block 250]. Like theabove-discussed bone models 22, the arthritic models 36 are located suchthat point P is at coordinates (X0-j, Y0-j, Z0-j) relative to the origin(X0, Y0, Z0) of the global coordinate system 63 [Block 190]. Thus, thebone and arthritic models 22, 36 share the same location and orientationrelative to the origin (X0, Y0, Z0) of the global coordinate system 63.This position/orientation relationship is generally maintainedthroughout the process discussed with respect to FIGS. 1E-1K.Accordingly, reorientations or movements relative to the origin (X0, Y0,Z0) of the bone models 22 and the various descendants thereof (i.e., therestored bone models 28, bone cut locations 30 and drill hole locations32) are also applied to the arthritic models 36 and the variousdescendants thereof (i.e., the jig models 38). Maintaining theposition/orientation relationship between the bone models 22 andarthritic models 36 and their respective descendants allows the “saw cutand drill hole data” 44 to be integrated into the “jig data” 46 to formthe “integrated jig data” 48 employed by the CNC machine 10 tomanufacture the customized arthroplasty jigs 2.

Computer programs for creating the 3D computer generated arthriticmodels 36 from the 2D images 16 include: Analyze from AnalyzeDirect,Inc., Overland Park, Kans.; Insight Toolkit, an open-source softwareavailable from the National Library of Medicine Insight Segmentation andRegistration Toolkit (“ITK”), www.itk.org; 3D Slicer, an open-sourcesoftware available from www.slicer.org; Mimics from Materialise, AnnArbor, Mich.; and Paraview available at www.paraview.org.

Similar to the bone models 22, the arthritic models 36 depict the bones18, 20 in the present deteriorated condition with their respectivedegenerated joint surfaces 24, 26, which may be a result ofosteoarthritis, injury, a combination thereof, etc. However, unlike thebone models 22, the arthritic models 36 are not bone-only models, butinclude cartilage in addition to bone. Accordingly, the arthritic models36 depict the arthroplasty target areas 42 generally as they will existwhen the customized arthroplasty jigs 2 matingly receive thearthroplasty target areas 42 during the arthroplasty surgical procedure.

As indicated in FIG. 1J and already mentioned above, to coordinate thepositions/orientations of the bone and arthritic models 22, 36 and theirrespective descendants, any reorientation or movement of the restoredbone models 28 from point P to point P′ is tracked to cause a generallyidentical displacement for the “arthritic models” 36 [Block 255]. Thus,for any change in the 3D position or orientation of the bone models 22or restored bone models 28 on account of any of the processes of [Blocks160, 165, 170] or any other position or orientation change to the bonemodels 22 or restored bone models 28 (e.g., the bone models 22 orrestored bone models 28 being reoriented at or moved from point P atcoordinates (X0-j, Y0-j, Z0-j) to point P′ at coordinates (X0-k, Y0-k,Z0-k)), an identical movement is caused in the 3D arthritic models 36such that the location and orientation of arthritic models 36 matchthose of the bone models 22 and restored bone models 28.

As depicted in FIG. 1J, computer generated 3D surface models 40 of thearthroplasty target areas 42 of the arthritic models 36 are importedinto computer generated 3D arthroplasty jig models 38 [Block 260]. Thus,the jig models 38 are configured or indexed to matingly (matchingly)receive the arthroplasty target areas 42 of the arthritic models 36.Jigs 2 manufactured to match such jig models 38 will then matinglyreceive the arthroplasty target areas of the actual joint bones duringthe arthroplasty surgical procedure.

In one embodiment, the procedure for indexing the jig models 38 to thearthroplasty target areas 42 is a manual process. The 3D computergenerated models 36, 38 are manually manipulated relative to each otherby a person sitting in front of a computer 6 and visually observing thejig models 38 and arthritic models 36 on the computer screen 9 andmanipulating the models 36, 38 by interacting with the computer controls11. In one embodiment, by superimposing the jig models 38 (e.g., femurand tibia arthroplasty jigs in the context of the joint being a knee)over the arthroplasty target areas 42 of the arthritic models 36, orvice versa, the surface models 40 of the arthroplasty target areas 42can be imported into the jig models 38, resulting in jig models 38indexed to matingly (matchingly) receive the arthroplasty target areas42 of the arthritic models 36. Point P′ (X0-k, Y0-k, Z0-k) can also beimported into the jig models 38, resulting in jig models 38 positionedand oriented relative to point P′ (X0-k, Y0-k, Z0-k) to allow theirintegration with the bone cut and drill hole data 44 of [Block 240].

In one embodiment, the procedure for indexing the jig models 38 to thearthroplasty target areas 42 is generally or completely automated, asdisclosed in U.S. patent application Ser. No. 11/959,344 to Park, whichis titled System and Method for Manufacturing Arthroplasty Jigs, wasfiled Dec. 18, 2007 and is incorporated by reference in its entiretyinto this Detailed Description. For example, a computer program maycreate 3D computer generated surface models 40 of the arthroplastytarget areas 42 of the arthritic models 36. The computer program maythen import the surface models 40 and point P′ (X0-k, Y0-k, Z0-k) intothe jig models 38, resulting in the jig models 38 being indexed tomatingly receive the arthroplasty target areas 42 of the arthriticmodels 36. The resulting jig models 38 are also positioned and orientedrelative to point P′ (X0-k, Y0-k, Z0-k) to allow their integration withthe bone cut and drill hole data 44 of [Block 240].

In one embodiment, the arthritic models 36 may be 3D volumetric modelsas generated from the closed-loop process discussed in U.S. patentapplication Ser. No. 11/959,344 filed by Park. In other embodiments, thearthritic models 36 may be 3D surface models as generated from theopen-loop process discussed in U.S. patent application Ser. No.11/959,344 filed by Park.

In one embodiment, the models 40 of the arthroplasty target areas 42 ofthe arthritic models 36 may be generated via an overestimation processas disclosed in U.S. Provisional Patent Application 61/083,053, which istitled System and Method for Manufacturing Arthroplasty Jigs HavingImproved Mating Accuracy, was filed by Park Jul. 23, 2008, and is herebyincorporated by reference in its entirety into this DetailedDescription.

As indicated in FIG. 1K, in one embodiment, the data regarding the jigmodels 38 and surface models 40 relative to point P′ (X0-k, Y0-k, Z0-k)is packaged or consolidated as the “jig data” 46 [Block 265]. The “jigdata” 46 is then used as discussed below with respect to [Block 270] inFIG. 1K.

As can be understood from FIG. 1K, the “saw cut and drill hole data” 44is integrated with the “jig data” 46 to result in the “integrated jigdata” 48 [Block 270]. As explained above, since the “saw cut and drillhole data” 44, “jig data” 46 and their various ancestors (e.g., models22, 28, 36, 38) are matched to each other for position and orientationrelative to point P and P′, the “saw cut and drill hole data” 44 isproperly positioned and oriented relative to the “jig data” 46 forproper integration into the “jig data” 46. The resulting “integrated jigdata” 48, when provided to the CNC machine 10, results in jigs 2: (1)configured to matingly receive the arthroplasty target areas of thepatient's bones; and (2) having cut slots and drill holes thatfacilitate preparing the arthroplasty target areas in a manner thatallows the arthroplasty joint implants to achieve a joint alignment thatis: (1) generally representative of the patient's pre-degenerative jointline (i.e., natural alignment); generally corresponding to a zeromechanical axis alignment; or (3) somewhere between (1) and (2),depending the input the physician provided in the process discussedabove with respect in FIG. 1I.

As can be understood from FIGS. 1A and 1K, the “integrated jig data” 48is transferred from the computer 6 to the CNC machine 10 [Block 275].Jig blanks 50 are provided to the CNC machine 10 [Block 280], and theCNC machine 10 employs the “integrated jig data” to machine thearthroplasty jigs 2 from the jig blanks 50 [Block 285].

For a discussion of example customized arthroplasty cutting jigs 2capable of being manufactured via the above-discussed process, referenceis made to FIGS. 2A-3B. While, as pointed out above, the above-discussedprocess may be employed to manufacture jigs 2 configured forarthroplasty procedures involving knees, elbows, ankles, wrists, hips,shoulders, vertebra interfaces, etc., the jig examples depicted in FIGS.2A-3B are for total knee replacement (“TKR”) or partial knee(“uni-knee”) replacement procedures. Thus, FIGS. 2A and 2B are,respectively, bottom and top perspective views of an example customizedarthroplasty femur jig 2A, and FIGS. 3A and 3B are, respectively, bottomand top perspective views of an example customized arthroplasty tibiajig 2B.

As indicated in FIGS. 2A and 2B, a femur arthroplasty jig 2A may includean interior side or portion 100 and an exterior side or portion 102.When the femur cutting jig 2A is used in a TKR procedure, the interiorside or portion 100 faces and matingly receives the arthroplasty targetarea 42 of the femur lower end, and the exterior side or portion 102 ison the opposite side of the femur cutting jig 2A from the interiorportion 100.

The interior portion 100 of the femur jig 2A is configured to match thesurface features of the damaged lower end (i.e., the arthroplasty targetarea 42) of the patient's femur 18. Thus, when the target area 42 isreceived in the interior portion 100 of the femur jig 2A during the TKRsurgery, the surfaces of the target area 42 and the interior portion 100match. In other words, the surface of the interior portion 100 of thefemur jig 2A is generally a negative of the target area 42 of thepatient's femur 18 and will matingly or matchingly receive the targetarea 42.

The surface of the interior portion 100 of the femur cutting jig 2A ismachined or otherwise formed into a selected femur jig blank 50A and isbased or defined off of a 3D surface model 40 of a target area 42 of thedamaged lower end or target area 42 of the patient's femur 18.

As indicated in FIGS. 3A and 3B, a tibia arthroplasty jig 2B may includean interior side or portion 104 and an exterior side or portion 106.When the tibia cutting jig 2B is used in a TKR procedure, the interiorside or portion 104 faces and matingly receives the arthroplasty targetarea 42 of the tibia upper end, and the exterior side or portion 106 ison the opposite side of the tibia cutting jig 2B from the interiorportion 104.

The interior portion 104 of the tibia jig 2B is configured to match thesurface features of the damaged upper end (i.e., the arthroplasty targetarea 42) of the patient's tibia 20. Thus, when the target area 42 isreceived in the interior portion 104 of the tibia jig 2B during the TKRsurgery, the surfaces of the target area 42 and the interior portion 104match. In other words, the surface of the interior portion 104 of thetibia jig 2B is generally a negative of the target area 42 of thepatient's tibia 20 and will matingly or matchingly receive the targetarea 42.

The surface of the interior portion 104 of the tibia cutting jig 2B ismachined or otherwise formed into a selected tibia jig blank 5013 and isbased or defined off of a 3D surface model 40 of a target area 42 of thedamaged upper end or target area 42 of the patient's tibia 20.

Another embodiment of the methods and systems for manufacturing the jigs2A, 2B will now be described, the another embodiment having a shorthanddesignation of “MA alignment”, wherein the embodiment described abovewith respect to FIGS. 1A-20 can have a shorthand designation of “naturalalignment”. The MA alignment embodiment is configured to provide apost-surgical joint alignment that is generally a zero mechanical axisalignment. For the MA alignment embodiment, the methods and systems formanufacturing the jigs 2A, 2B are generally the same as described abovewith respect to the natural alignment embodiment, except the POP for theMA alignment embodiment does not first calculate a post-surgical jointalignment that is (1) generally representative of the patient'spre-degenerative joint line and then allowing the surgeon to keep suchan alignment or modify the alignment to correspond (2) generally to azero mechanical axis alignment or (3) an alignment that is somewherebetween (1) and (2). Instead, the MA alignment embodiment has POP thatfirst achieves a post-surgical joint alignment that is generallyrepresentative of a zero mechanical axis alignment and then allows thesurgeon to keep such an alignment or modify the alignment as desired.

The MA alignment embodiment begins by following generally the sameprocess as described above with respect to FIGS. 1A-1E, arriving atBlock 145 and Block 245 of FIG. 1E, wherein the knee coil 2D images 16are segmented along bone boundaries to generate 2D bone-only contourlines [Block 145] and segmented along cartilage and bone boundaries togenerate 2D bone and cartilage contour lines [Block 245]. As can beunderstood from FIGS. 1F and 1J, the 2D bone-only contour lines are thenused to generate the 3D bone models (i.e., planning models) 22 [Block150], and the 2D bone and cartilage contour lines are used to generatethe 3D bone and cartilage models (i.e., arthritic models) 36 [Block250]. Before being used to generate the 3D arthritic models 36, the 2Dbone and cartilage contour lines generated during Block 245 aresubjected to an overestimation process as disclosed in U.S.Non-Provisional patent application Ser. No. 12/505,056, which is titledSystem and Method for Manufacturing Arthroplasty Jigs Having ImprovedMating Accuracy, was filed by Park Jul. 17, 2009, and is herebyincorporated by reference in its entirety into this DetailedDescription.

FIG. 21 shows an example of 3D bone models 22 resulting from the 2Dbone-only contour lines. FIG. 22 shows an example of the 3D arthriticmodels 36 resulting from the overestimated 2D bone and cartilage contourlines. Due to the overestimation process applied to the bone andcartilage contour lines, surfaces of the arthritic models 36 areoverestimated (i.e., pushed outwardly from the interior of the model 36)in regions of the model 36 that correspond to (1) regions of the imagesthat are associated with low accuracy due to limitations in the imagingprocesses or (2) regions of the model that are unlikely to bemanufactured accurately into a jig blank due to limitations of, forexample, the milling process.

As can be understood from FIGS. 23 and 24, which are, respectively,coronal and axial views of the models 22, 36 of the femur 18, thefemoral models 22, 36 are superimposed to begin the POP process of theMA alignment embodiment. Similarly, as can be understood from FIGS. 25and 26, which are, respectively, coronal and axial views of the models22, 36 of the tibia 20, the tibial models 22, 36 are superimposed tobegin the POP process of the MA alignment embodiment. In other words,POP for the MA alignment embodiment employs both the bone models 22 andthe arthritic models 36. The bone models 22 identify the cortical andsubchondral bone boundaries, and the arthritic models 36 identify thecartilage boundaries. By employing both types of models 22, 36, the fulldefinition of the knee anatomy is achieved with distinct cartilage andbony anatomical landmarks for the femur 18 and tibia 20. From here on inthis discussion regarding the MA alignment embodiment, the models 22, 26when superimposed together for purposes of POP will be referred to assuperimposed models 100.

As indicated in FIG. 23, a most distal femoral condylar point 105 isidentified on each of the condyles of the femoral arthritic model 36 ofthe femoral superimposed model 100. Similarly, as indicated in FIG. 24,a most posterior point 107 is identified on each of the condyles of thefemoral arthritic model 36 of the femoral superimposed model 100. Aposterior condylar line 108 connects the most posterior condylar points107.

As indicated in FIG. 25, a most proximal tibial condylar point 110 isidentified on each of the condyles of the tibial arthritic model 36 ofthe tibial superimposed model 100. As indicated in FIG. 26, a centerpoint 111 of the tibial plateau and a point 112 at the medial third ofthe tibial tuberosity are identified on the bone model 22 of the femoraltibial superimposed model 100. A rotational tibial reference line 113connects the points 111 and 112.

As can be understood from FIG. 1L, the hip, knee and ankle center points54, 56, 57, 58 and the femoral mechanical axis 68, tibial mechanicalaxis 70 and mechanical axis 72 are depicted in 3D with the 3Dsuperimposed models 100 presented in a coronal view [Block 1000]. Thecenter points 54, 56, 57 and 58 are obtained and positionally referencedto the models 100 as discussed above with respect to FIGS. 1A-1E.

As can be understood from FIG. 1L, a most distal point 305 of the twodistal femoral condylar points 105 identified in FIG. 23 is identified,and a line 300 orthogonal to the femoral mechanical axis 68 andintersecting the most distal femoral condylar point 305 is provided[Block 1005]. Similarly, a most proximal point 315 of the two proximaltibial condylar points 110 identified in FIG. 25 is identified, and aline 310 orthogonal to the tibial mechanical axis 70 and intersectingthe most proximal tibial condylar point 305 is provided [Block 1005].

As indicated in FIG. 1L, a femoral resection plane 320 and a tibialresection plane 325 are determined by setting a depth of resection DRoff of each orthogonal line 300, 310, the femoral and tibial resectionplanes 320, 325 being respectively orthogonal to the femoral mechanicalaxis 68 and the tibial mechanical axis 70 in the coronal view [Block1010]. The superior/inferior translation is now established for the POP.

In one embodiment, the depth of resection DR for the femur may beapproximately 8 mm, plus or minus 1-3 mm depending on the depth of theimplant intended to be implanted. For example, the depth of resection DRfor the femur may be based on the thickness of the femoral implant formthe most distal point of the medial or lateral condyle to the other sideof the flange.

In one embodiment, the depth of resection DR for the tibia may beapproximately 11 mm, plus or minus 1-3 mm depending on the depth of theimplant intended to be implanted. For example, the depth of resection DRfor the tibia may be based on the thickness of the tibia implant formthe most proximal point of the medial or lateral condyle to the otherside of the base plate and its liner.

FIG. 27 is an enlarged coronal view of the femoral bone model 22illustrating the results of the operations of Blocks 1000-1010 in FIG.1L with respect to the femur 18. FIG. 28 is an enlarged coronal view ofthe tibial superimposed model 100 illustrating the results of theoperations of Blocks 1000-1010 in FIG. 1L with respect to the tibia 18.

As can be understood from FIG. 29, which is a sagittal view of thefemoral bone model 22, the femoral resection plane 320 is caused to beorthogonal to the femoral mechanical axis 68 in the sagittal view.Similarly, as can be understood from FIG. 30, which is a sagittal viewof the tibial superimposed model 100, the tibial resection plane 325 iscaused to be orthogonal to the tibial mechanical axis 70 in the sagittalview. The flexion/extension orientations for both the femur 18 and tibia20 have now been established for the POP. Variations toflexion/extension orientation can be made via the implant sizingoperations as described below.

As indicated in FIG. 31, which is the same axial view of the femursuperimposed model 100 as shown in FIG. 24, an external rotation ofapproximately three degrees (plus or minus a degree or so, depending onthe implant intended to be implanted) is provided, as can be understoodfrom the angular difference between lines 108 and 109. Specifically, theimplant is rotated externally the desired amount from the previouslyidentified posterior condylar line 108 about the center of the implant.The internal/external rotational orientation for the femur 18 has nowbeen established for the POP.

As can be understood from FIG. 26, external rotation can be visualizedoff of the medial one third of the tibial tubercle identified by point112. Specifically, from the previously identified tibial rotationalreference (i.e., the medial one third of the tibial tubercle indicatedby point 112), the tibial implant is aligned with the rotationalreference. The internal/external rotational orientation for the tibia 20has now been established for the POP.

As shown in FIG. 1M, 3D arthroplasty femoral and tibial implant models34 are respectively superimposed on the femur portion 18 and tibiaportion 20 of the superimposed models 100 [Block 1015]. In doing so, theresection plane 330 of each implant model 34 is aligned with therespective resection line 320, 325 and orthogonal to the respectivemechanical axis 68, 70. Since the depth of resection DR is based off ofthe dimension of the candidate implant, the condylar surfaces of eachimplant model 34 end up being positioned adjacent the correspondingcondylar surfaces of the superimposed models 100 [Block 1015].

For example, as shown in FIGS. 32 and 33, which are, respectively,coronal and sagittal views of the femoral bone model 22 of thesuperimposed model 100, in one embodiment, the resection plane 330 ofthe femoral implant model 34 includes the resection line 320, thefemoral implant resection plane 330 being orthogonal to the femoralmechanical axis 68. Also, the resection line 320 via the above-describedoperation of Block 1010 of FIG. 1L is located such that the condylarsurfaces of the femoral implant model 34 are adjacent the condylarsurfaces of the femoral bone model 22 and, in some cases, essentiallycoextensive with each other over portions of the condylar surfaces.

Similarly, as can be understood from FIG. 34, which is a sagittal viewof the tibial bone model 22 of the superimposed model 100, in oneembodiment, the resection plane 330 of the tibial implant model 34includes the resection line 325 (shown as a point), the tibial implantresection plane 330 being orthogonal to the tibial mechanical axis 70.Also, the resection line 325 via the above-described operation of Block1010 of FIG. 1L is located such that the condylar surfaces of the tibialimplant model 34 are adjacent the condylar surfaces of the tibial bonemodel 22 and, in some cases, essentially coextensive with each otherover portions of the condylar surfaces.

As can be understood from FIG. 35, which is an axial view of the femoralimplant model 34 superimposed on the femoral bone model 22, the femoralimplant model 34 is centered medial-lateral relative to the femoral bonemodel 22 to have symmetric medial-lateral overhang, thereby completingthe medial-lateral translation of the implant model. Similarly, as canbe understood from FIG. 36, which is an axial view of the tibial implantmodel 34 superimposed on the tibial bone model 22, the tibial implantmodel 34 is centered medial-lateral and anterior-posterior relative tothe tibial bone model 22 to have equal bone exposed circumferentially,the size of the tibial implant model 34 being adjusted as necessary,thereby completing the medial-lateral translation and theanterior-posterior translation of the implant model.

Femoral implant model sizing may be completed by first sizing thefemoral implant model 34 in the sagittal view so as to fit the distalcondyles and anterior cortex of the femoral bone model 22. Inspectionsfor fit are made in the coronal and axial views. The best implant sizeis determined based on the distance from the posterior condylar line tothe anterior cortex. If notching of the femoral shaft is present, thefemoral implant model 34 flexed up to a maximum of approximately fivedegrees and reassessed for notching. If notching is still present, thenthe femoral implant model 34 is upsized and returned to a neutralalignment. If notching is again present, then the femoral implant model34 is flexed up to a maximum of approximately five degrees and themedial-lateral overhang is assessed and a size for the femoral implantmodel is selected.

As can be understood from FIG. 33, the posterior position of the femoralimplant model 34 is maintained relative to the femoral bone model 22while the anterior-posterior position is modified by increasing ordecreasing the size of the femoral implant model 34. This completes theanterior-posterior translation of the femoral implant model.

As can be understood from FIG. 1M, in one embodiment, the orientation offemur and tibia aspects of superimposed models 100, 34 are adjusted soresections 320, 325 are generally parallel, the condylar surfaces ofeach implant model 34 generally correspond relative to each other, andthe femoral and tibial mechanical axes 68, 70 generally align with themechanical axis 72 [Block 1020]. Similar to described above with respectto Block 195 of FIG. 1H, the various models and axes depicted asdescribed in Block 1020 may be sent to the physician as a coronal viewsnapshot for review. In a manner similar to that described above withrespect to FIG. 1I, the physician may review the provided coronal viewsnapshot and accept the POP as depicted therein or propose modificationsto the POP. Once the POP is approved by the physician, the POP isemployed as saw cut and drill hole data 44 [Block 240 of FIG. 1K] andthen combined with the jig data 46 to form integrated jig data 48 [Block270 of FIG. 1K], the manufacture of the jigs 2A, 2B then preceding asdescribed in Blocks 275-285 of FIG. 1K.

The discussion provided herein is given in the context of TKR and TKRjigs and the generation thereof. However, the disclosure provided hereinis readily applicable to uni-compartmental or partial arthroplastyprocedures in the knee or other joint contexts. Thus, the disclosureprovided herein should be considered as encompassing jigs and thegeneration thereof for both total and uni-compartmental arthroplastyprocedures.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

We claim:
 1. A method of preoperatively planning a knee arthroplasty,the method comprising: identify first locations of landmarks in firstmedical images of a first resolution; identify second locations of thelandmarks in second medical images of a second resolution beingdifferent than the first resolution; identifying in at least one coronalview of the second medical images a hip center and an ankle center;causing the first medical images and second medical images to match eachother with respect to location and orientation in a computer globalcoordinate system; generating a computerized three dimensional bonemodel from data associated with the first medical images; and applying acomputerized representation of an implant to the computerized threedimensional bone model to determine an arthroplasty resection.
 2. Themethod of claim 1, wherein the first medical images and the secondmedical images are caused to match each other with respect to locationand orientation in a computer global coordinate system by running atransformation with the first and second locations.
 3. The method ofclaim 2, wherein the transformation comprises an Iterative Closest Pointalgorithm or gradient descent optimization.
 4. The method of claim 2,wherein the transformation causes the first medical images to repositionin the computer global coordinate system to match the location andorientation of the second medical images.
 5. The method of claim 1,further comprising identifying in at least one coronal view of thesecond medical images a knee center.
 6. The method of claim 1, furthercomprising conducting a joint analysis wherein the position of thecomputerized three dimensional bone model in the computer globalcoordinate system is manipulated to adjust a joint gap of the bonemodel.
 7. The method of claim 6, wherein the joint gap is adjusted suchthat a medial joint gap is equal to a lateral joint gap.
 8. The methodof claim 1, wherein the computerized representation of the implantcomprises a computerized three dimensional model of the implant.
 9. Themethod of claim 8, wherein the implant comprises at least one of afemoral knee implant or a tibial knee implant.
 10. The method of claim1, further comprising determining in the computer global coordinatesystem an arthroplasty resection relative to anatomical informationresulting from the first medical images subsequent to the first andsecond medical images being caused to match each other with respect tolocation and orientation in the computer global coordinate system.
 11. Amethod of preoperatively planning a knee arthroplasty, the methodcomprising: identify first locations of landmarks in first medicalimages of a first resolution; identify second locations of the landmarksin second medical images of a second resolution being different than thefirst resolution; causing the first medical images and second medicalimages to match each other with respect to location and orientation in acomputer global coordinate system; and determining in the computerglobal coordinate system an arthroplasty resection relative toanatomical information resulting from the first medical imagessubsequent to the first and second medical images being caused to matcheach other with respect to location and orientation in the computerglobal coordinate system, wherein determining in the computer globalcoordinate system the arthroplasty resection relative to the anatomicalinformation comprises applying a computerized representation of animplant to the anatomical information.
 12. The method of claim 11,wherein the computerized representation comprises a computerized threedimensional model of the implant.
 13. The method of claim 12, whereinthe implant comprises at least one of a femoral knee implant or a tibialknee implant.
 14. The method of claim 11, wherein the anatomicalinformation comprises a computerized three dimensional bone modelgenerated from the first medical images of the matched first and secondmedical images.
 15. The method of claim 11, further comprising sendingdata to a computer guided cutting machine, the data pertaining to anorientation and location of the arthroplasty resection.
 16. The methodof claim 1, further comprising determining in the computer globalcoordinate system an arthroplasty resection relative to anatomicalinformation resulting from the second medical images subsequent to thefirst and second medical images being caused to match each other withrespect to location and orientation in the computer global coordinatesystem.
 17. The method of claim 16, wherein the anatomical informationcomprises a mechanical axis defined from the second medical images ofthe matched first and second medical images.
 18. The method of claim 17,wherein the mechanical axis is defined at least in part from at leastone of a hip center or an ankle center identified in the second medicalimages.
 19. The method of claim 18, wherein determining the arthroplastyresection relative to the anatomical information comprises determining adesired orientation of the arthroplasty resection relative to themechanical axis.
 20. The method of claim 19, wherein the desiredorientation is a zero degree mechanical axis orientation.
 21. A methodof preoperatively planning a knee arthroplasty, the method comprising:identify first locations of landmarks in first medical images of a firstresolution; identify second locations of the landmarks in second medicalimages of a second resolution being different than the first resolution;causing the first medical images and second medical images to match eachother with respect to location and orientation in a computer globalcoordinate system; determining in the computer global coordinate systeman arthroplasty resection relative to anatomical information resultingfrom the second medical images subsequent to the first and secondmedical images being caused to match each other with respect to locationand orientation in the computer global coordinate system, wherein theanatomical information comprises a mechanical axis defined from thesecond medical images of the matched first and second medical images,wherein the mechanical axis is defined at least in part from at leastone of a hip center or an ankle center identified in the second medicalimages, wherein determining the arthroplasty resection relative to theanatomical information comprises determining a desired orientation ofthe arthroplasty resection relative to the mechanical axis, wherein thedesired orientation is a zero degree mechanical axis orientation; andsending data to a computer guided cutting machine, the data pertainingto an orientation and location of the arthroplasty resection.
 22. Themethod of claim 17, wherein the mechanical axis is defined from a hipcenter, knee center, and an ankle center identified in the secondmedical images.
 23. The method of claim 22, wherein at least one of ahip, knee or ankle centers is determined from at least one of a sagittalor axial view.
 24. The method of claim 22, wherein determining thearthroplasty resection relative to the anatomical information comprisesdetermining a desired orientation of the arthroplasty resection relativeto the mechanical axis.
 25. The method of claim 24, wherein the desiredorientation is a zero degree mechanical axis orientation.
 26. The methodof claim 24, further comprising sending data to a computer guidedcutting machine, the data pertaining to an orientation and location ofthe arthroplasty resection.
 27. The method of claim 1, wherein themedical images are generated via at least one of CT, MRI or othermedical imaging methods.
 28. The method of claim 1, wherein the firstmedical images include a region including a knee and the second medicalimages includes at least one of the knee region, a hip or an ankle. 29.The method of claim 2, wherein the landmarks in the first medical imagesare knee landmarks.
 30. The method of claim 29, wherein the kneelandmarks comprise at least one of a center of a femur condyle regionnear a trochlear groove, a medial point of a medial femur epicondyle, ora lateral point of a lateral femur epicondyle.
 31. The method of claim30, wherein the medial point of the medial femur epicondyle is the mostmedial point.
 32. The method of claim 30, wherein the lateral point ofthe lateral femur epicondyle is the most lateral point.
 33. The methodof claim 29, wherein the knee landmarks comprise at least one of amedial edge of a medial tibial condyle, a lateral edge of a lateraltibial condyle, a medial transition from a medial tibial plateau to atibial shaft, or a lateral transition from a lateral tibial plateau tothe tibial shaft.
 34. A method of preoperatively planning a kneearthroplasty, the method comprising: identify first locations oflandmarks in first medical images of a first resolution; identify secondlocations of the landmarks in second medical images of a secondresolution being different than the first resolution; causing the firstmedical images and second medical images to match each other withrespect to location and orientation in a computer global coordinatesystem; and determining in the computer global coordinate system a holerelative to the anatomical information resulting from the matched firstand second medical images.
 35. The method of claim 34, whereindetermining in the computer global coordinate system the hole comprisesapplying a computerized representation of the implant to the anatomicalinformation resulting from the first medical images of the matched firstand second medical images.
 36. The method of claim 35, wherein thecomputerized representation comprises a computerized three dimensionalmodel of the implant.
 37. The method of claim 36, wherein the anatomicalinformation comprises a computerized three dimensional bone modelgenerated from the first medical images of the merged first and secondmedical images.
 38. The method of claim 36, wherein the implantcomprises at least one of a femoral knee implant or a tibial kneeimplant.
 39. The method of claim 1, wherein the second resolution isless than the first resolution.
 40. The method of claim 11, wherein thesecond resolution is less than the first resolution.
 41. The method ofclaim 21, wherein the second resolution is less than the firstresolution.
 42. The method of claim 34, wherein the second resolution isless than the first resolution.